1. Field of the Invention
The present invention relates to a thermoplastic resin composition, a process for production thereof, and a film produced from said composition. More particularly, the present invention relates to a thermoplastic resin composition obtained by kneading a thermoplastic resin and particular inorganic particles using a vented double-screw kneader and extruder, a process for production thereof, and a biaxially oriented film produced from said composition.
2. Prior Art
Thermoplastic resins, particularly aromatic polyesters have excellent physical and chemical properties and are therefore used in a large amount in the fields of fiber, film, resin, etc. Meanwhile, they are known to arouse, in producing a molded product therefrom or in handling the molded product, a problem of reduction in workability, productivity or product value, caused by inferior slipperiness.
For such a problem, it was proposed to add fine particles to a thermoplastic resin to produce a molded product having appropriate surface unevenness and improved slipperiness. As the fine particles, there are being used inorganic particles of, for example, silica, titanium dioxide, calcium carbonate, talc or kaolinite. In adding inorganic particles, however, the presence of large particles therein poses a problem. The presence of large particles causes, in the case of, for example, a film for magnetic tape, reduction in electromagnetic transduction property or drop out and impairs important film qualities. To remove such large particles, it is generally conducted, in adding inorganic particles during polymer synthesis, to convert the inorganic particles into a slurry or solution, subject the slurry or solution to grinding and sifting, and then add the resulting material. This operation, however, requires a large cost and a long time for slurry formation, grinding and sifting; moreover, when the particles after the above operation are added during polymer synthesis, the particles cause reagglomeration and it is impossible to completely prevent the incoming of large particles. In recent years, it has been conducted to produce various kinds of value-added polymers from a single master polymer. In this case, addition of particles during polymer synthesis incurs a big operational loss when the kind of particles used is changed.
Hence, there were proposed, for example, a method which comprises kneading powdery particles into a polyester using a single-screw extruder or a double-screw kneader and extruder (JP-A-1-157806), or a method which comprises adding, to a polyester, a liquid slurry of particles dispersed in a medium (JP-A-6-91635). When these methods are applied to inorganic particles, however, insufficient disintegration of agglomerated particles or large particles takes place if the shear stress applied is insufficient, resulting in inferior dispersion of particles in resin; if the shear stress is too high, excessive disintegration of particles takes place, resulting in decreased particle sizes, and the intended slipperiness, etc. are not achieved.
When the inorganic particles are, in particular, silica particles, the silica particles agglomerate easily because they have a large number of silanol groups on the surfaces. When the above-mentioned methods are applied to silica particles, insufficient disintegration of agglomerated particles or large particles takes place if the shear stress applied is insufficient, resulting in inferior dispersion of particles in resin; if the shear stress is too high, excessive disintegration of particles takes place, resulting in decreased particle sizes, the intended slipperiness, etc. are not achieved, and excessive disintegration further incurs reagglomeration and formation of large particles.
To prevent the agglomeration of silica particles, it is generally conducted to treat a silica powder with a silicon-containing organic compound. The silica powder treated with a silicon-containing organic compound is already in commercial production and is in use in various applications.
When the above-mentioned methods are applied to the silica powder treated with a silicon-containing organic compound, the silica powder is easily dispersed in non-polar solvents for its hydrophobicity but is very difficult to disperse in polar solvents.
The present inventors made a study in order to alleviate the above-mentioned drawbacks of the conventional method for addition of particles and produce a thermoplastic resin film superior particularly in slipperiness and surface uniformity. As a result, the present invention has been completed.
An object of the present invention is to provide a thermoplastic resin composition wherein inorganic particles are easily synthesized in a thermoplastic resin, whereby particles in the obtained thermoplastic resin have good dispersibility, and a process for production of such a composition.
Other object of the present invention is to provide a biaxially oriented film produced, by the above process, from a thermoplastic resin composition wherein inorganic particles are contained in good dispersibility.
According to the study made by the present inventors, the above object of the present invention is achieved by a thermoplastic resin composition containing inorganic particles, wherein (i) the inorganic particles have pore volume of 0.1 to 3 ml/g and (ii) the inorganic particles are treated at the surfaces with a hydrophilic polyester of 0.05 to 10 times the weight of the inorganic particles or with a silicon-containing organic compound.
The above thermoplastic resin composition of the present invention is classified into the following compositions (a) and (b), based on the kind of the compound used for surface treatment of inorganic particles.
(a) A thermoplastic resin composition containing inorganic particles, wherein (i) the inorganic particles have pore volume of 0.1 to 3 ml/g and (ii) the inorganic particles are treated at the surfaces with a hydrophilic polyester of 0.05 to 10 times the weight of the inorganic particles.
(b) A thermoplastic resin composition containing silica particles, wherein (i) the silica particles have pore volume of 0.1 to 3 ml/g and (ii) the inorganic particles are treated at the surfaces with a silicon-containing organic compound.
The study by the present inventors further found out that the above thermoplastic resin composition can be produced by a process for producing a thermoplastic resin composition by kneading a thermoplastic resin and inorganic particles using a vented double-screw kneader and extruder, in which process (i) the inorganic particles have pore volume of 0.1 to 3 ml/g, (ii) the inorganic particles are treated at the surfaces with a hydrophilic polyester of 0.05 to 10 times the weight of the inorganic particles or with a silicon-containing organic compound, and the inorganic particles are fed into the vented double-screw kneader and extruder in the form of their dispersion in water and/or an inert organic solvent.
The present invention is described below in more detail.
As the thermoplastic resin constituting the composition of the present invention, there are mentioned a polyethylene, a polypropylene, polyamides, polyesters, and the like. Of these, an aromatic polyester is preferred.
As the aromatic polyester, an aromatic polyester composed of an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component is particularly preferred. The aromatic dicarboxylic acid can be exemplified by terephthalic acid, 2,6-naphthalenedicarboxylic acid and 4,4xe2x80x2-diphenyldicarboxylic acid. Of these, terephthalic acid or 2,6-naphthalenedicarboxylic acid is preferred. The aliphatic glycol can be exemplified by ethylene glycol, propylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol. Of these, ethylene glycol is preferred.
The polyester is preferably a homopolymer composed of the above aromatic dicarboxylic acid component and the above aliphatic glycol component, but the polyester may be a copolymer containing a third component in a small amount. The third component can be exemplified, when the main component is ethylene terephthalate, by diols such as diethylene glycol, propylene glycol, neopentyl glycol, polyalkylene glycol, 1,4-cyclohexanedimethanol and the like; dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and the like; and polyfunctional polycarboxylic acids such as trimellitic acid, pyromellitic acid and the like. When the main component is ethylene 2,6-naphthalate, there can be mentioned the same third components as mentioned above, except that 2,6-naphthalenedicarboxylic acid is converted to terephthalic acid.
As to the thermoplastic resin used in the present invention, there is no particular restriction as long as it can be efficiently produced by a known method or a method whose techniques have been accumulated in the industry. The thermoplastic resin may contain, as necessary, a metal-based catalyst, for example, a compound of lithium, sodium, calcium, magnesium, manganese, zinc, antimony, germanium, titanium or the like, and additives such as phosphorus compound (as stabilizer) and the like.
The inorganic particles also constituting the present thermoplastic resin composition have pore volume of 0.1 to 3 ml/g, preferably 0.3 to 2.5 ml/g. When inorganic particles having pore volume larger than 3 ml/g are used, the resulting thermoplastic resin composition gives a film of insufficient slipperiness and low handleability. When inorganic particles having pore volume smaller than 0.1 ml/g are used, the cost for producing such particles is high, leading to the high cost of molded product. Therefore, such inorganic particles are not desired.
As to the inorganic particles used in the present invention, there is no particular restriction. As preferred specific examples of the inorganic particles, there can be mentioned silica, titanium dioxide, calcium carbonate, talc and kaolinite. Of these, silica is suitable. The average particle diameter of these inorganic particles is 0.03 to 5 xcexcm, preferably 0.05 to 3 xcexcm. When the average particle diameter is smaller than 0.03 xcexcm, the travelling property and abrasion resistance of the film obtained are insufficient. When the average particle diameter is larger than 5 xcexcm, the film obtained has too large a surface roughness or low transparency. Therefore, such average particle diameters are not preferred.
The inorganic particles used in the present invention have no particular restriction as to the production process, the shape or the like. The present invention is effective even to inorganic particles which have a number of silanol groups on the surfaces and thereby cause dehydration and condensation during kneading with a thermoplastic resin to form large particles, such as amorphous silica produced by wet process.
In the present invention, the amount of the inorganic particles added to the thermoplastic resin is preferably 0.01 to 10% by weight, more preferably 0.01 to 5% by weight to the thermoplastic resin. When the amount is larger than 10% by weight, no sufficient dispersibility is obtained. When the shear stress applied is increased for higher dispersion, disintegration of particles and reduction in particle size take place; consequently, when, for example, a film is produced, the film has an increased friction coefficient and low handleability. When the amount is smaller than 0.01% by weight, the effect of particles addition is not sufficient.
As mentioned previously, the inorganic particles contained in the thermoplastic resin of the present invention, preferably have an average particle diameter of 0.03 to 5 xcexcm. Further preferably, the inorganic particles have at least two peaks in the particle size distribution. When the peaks in the particle size distribution are two, the difference in particle diameter between the two peaks is preferably 0.3 xcexcm or more, more preferably 0.5 xcexcm or more. When the peaks in the particle size distribution are three or more, the difference in particle diameter between the maximum peak having the largest height and the minimum peak having the smallest height is preferably the same as mentioned for the above case of two peaks.
In the present invention, the peak(s) in the particle size distribution of the inorganic particle can be determined from a frequency distribution wherein the particle frequency to the particle diameter of inorganic particles is expressed as the area of particles, obtained by, for example, a laser diffraction method and/or an observation method using an electron microscope (the both methods are described later). In the present invention, xe2x80x9ca plurality of peaksxe2x80x9d refer to such a case that there are, in the frequency distribution, at least two peaks (one of these peaks is the maximum height peak), there is, between the maximum peak and other peak(s), at least one valley whose height is 70% or less of the height of the maximum peak, and the height(s) of the other peak(s) is (are) 10% or more of the height of the maximum peak.
In the present invention, the inorganic particles are used after having been treated, at the surfaces, with a hydrophilic polyester or with a silicon-containing organic compound.
First, description is made on the surface treatment of the inorganic particles with a hydrophilic polyester.
In the present invention, the amount of the hydrophilic polyester used for the surface treatment of the inorganic particles is necessarily 0.05 to 10 times in weight (5 to 1,000% by weight) to the inorganic particles, preferably 0.3 to 8 times in weight (30 to 800% by weight), particularly preferably 0.5 to 6 times in weight (50 to 600% by weight). When the amount of the hydrophilic polyester is less than 0.05 time in weight to the inorganic particles, the inorganic particles cause agglomeration and, therefore, when a thermoplastic resin containing such inorganic particles is molded into, for example, a film, large particles are formed in the film. When the amount is larger than 10 times in weight, the dispersion of such inorganic particles has a very high viscosity, making very difficult the quantitative feeding of the dispersion into a vented double-screw kneader and extruder, and the film obtained has a high haze and low transparency.
The operation of the surface treatment of the inorganic particles with the hydrophilic polyester can be conducted at any desired step as long as the step is before the kneading of the inorganic particles with the thermoplastic resin, that is, before the feeding of the inorganic particles into a vented double-screw kneader and extruder.
The hydrophilic polyester used for the surface treatment of the inorganic particles can be any water-soluble or water-dispersible polyester. That is, the hydrophilic polyester is a polyester which can be dissolved and/or finely dispersed in a liquid medium described later. The acid component constituting the hydrophilic polyester can be exemplified by polycarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4xe2x80x2-diphenyldicarboxylic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, succinic acid, 5-sodiumsulfoisophthalic acid, 2-pottasiumsulfoterephthalic acid, trimellitic acid, trimesic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, monopotassium salt of trimellitic acid and the like. The hydroxy compound component can be exemplified by polyhydroxy compounds such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylene glycol, ethylene oxide adduct of bisphenol A, propylene oxide adduct of bisphenol A, diethylene glycol, triethylene glycol, polyethylene oxide glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerine, trimethylolpropane, sodium dimethylolethylsulfonate, potassium dimethylolpropionate and the like. A hydrophilic polyester can be produced from these compounds by a per se known process. That is, a polycarboxylic acid and a polyhydroxy compound are subjected to ester interchange, followed by polycondensation at a high temperature under reduced pressure; or, an ester-forming derivative of a polycarboxylic acid and a polyhydroxy compound are subjected to ester interchange, followed by polycondensation at a high temperature under reduced pressure; thereby, a hydrophilic polyester can be produced. In order to produce a hydrophilic polyester favorably, it is preferred to allow the polyester to contain therein a sulfonic acid salt group-containing compound. The sulfonic acid salt group-containing compound includes metal salts of sulfoisophthalic acid, sulfoterephthalic acid, sulfonaphthalene-2,6-dicarboxylic acid, ester-forming derivative thereof, etc. As the preferable metal of the metal salts, there can be mentioned sodium, lithium, potassium, magnesium, etc. Use of 5-sodiumsulfoisophthalic acid is preferred particularly. The content of the sulfonic acid salt group-containing compound in the acid component is in a range of preferably 0.1 to 30 mole %, more preferably 0.1 to 15 mole %. When the content is lower than 0.1 mole %, the water solubility or dispersibility of the hydrophilic polyester is insufficient. When the content is higher than 30 mole %, the thermal stability when a thermoplastic resin was formed, is inferior. Such a hydrophilic polyester may be a self-crosslinking type having functional group in the molecule, or may be crosslinked using a curing agent such as melamine resin, epoxy resin or the like.
In the present invention, there is no particular restriction as to the method for surface treatment of the inorganic particles with the hydrophilic polyester. However, preferred is, for example, a method which comprises dissolving and/or finely dispersing a hydrophilic polyester in a medium and then mixing thereinto inorganic particles to form a slurry.
As to the medium for the hydrophilic polyester, there is no particular restriction, and a known medium can be used. However, water and/or a mixed liquid consisting of water and an organic solvent is preferred from the standpoint of safety. As the organic solvent in the mixed liquid, an organic solvent capable of dissolving the hydrophilic polyester is preferred. The content of the organic solvent is preferably 3% by weight or less, more preferably 1% by weight or less to the total of the liquid medium and the hydrophilic polyester. There is no particular restriction as to the method for preparing a solution composed mainly of a hydrophilic polyester, and a generally known method can be used. For example, a hydrophilic polyester is dissolved in hot water with stirring; or, a hydrophilic polyester is dissolved in a hydrophilic organic solvent which has a water solubility of 20 g or more per liter of water, at 20xc2x0 C. and has a boiling point of 100xc2x0 C. or less or shows azeotropy with water at 100xc2x0 C. or less. The organic solvent can be exemplified by dioxane, acetone, tetrahydrofuran and methyl ethyl ketone. To the thus-obtained hydrophilic polyester solution can be added a small amount of a surfactant in order to promote the dissolution and/or fine dispersion of the hydrophilic polyester. To the solution is added water with stirring, priferably with high-speed stirring under heating, to obtain an aqueous solution. This aqueous solution can also be obtained by adding the hydrophilic polyester solution to water being stirred. The aqueous solution is subjected to separation and removal of the organic solvent. For example, hydrophilic organic solvent removal is conducted at ordinary pressure or under reduced pressure, whereby an intended aqueous polyester solution is obtained.
As the above-mentioned surfactant, a known surfactant can be used. There can be mentioned, for example, a polyoxyethylene alkylphenyl ether, a polyoxyethylene-fatty acid ester, a sorbitan-fatty acid ester, a glycerine-fatty acid ester, a metal soap of a fatty acid, an alkylsulfuric acid salt, an alkylsulfonic acid salt, an alkylsulfosuccinic acid salt, quaternary ammonium chloride, an alkylamine hydrochloride and sodium dodecylbenzenesulfonate.
There is no particular restriction as to the method for converting the inorganic particles into a slurry. It is possible to conduct grinding or disintegration and then sieving, or conduct sieving and then grinding or disintegration. Or, it is possible to subject inorganic particles to grinding or disintegration and/or sieving by a dry method and then convert the resulting inorganic particles into a slurry using the above-mentioned aqueous polyester solution. Or, a dry method and a wet method may be combined appropriately. For example, inorganic particles may be ground by a dry method and then converted into a slurry, and the slurry may be subjected to sieving by a wet method; or, inorganic particles may be disintegrated and/or sieved by a dry method and the resulting inorganic particles may be subjected to grinding by a wet method.
In order to obtain a uniform slurry, a dispersant, an anti-foaming agent, etc. may be added as long as the effect of the present invention is not impaired. Specific examples of these additives are sodium polystyrenesulfonate, sodium polyacrylate, carboxymethyl cellulose, a polyvinyl alcohol, a salt of a copolymer of a vinyl compound and a carboxylic acid type monomer, a partial alkyl ester of a polyacrylic acid, a polyalkylenepolyamine, ammonia, ammonia salts, sodium hydroxide, sodium salts such as sodium hexametaphosphate and sodium pyrophosphate, onium compounds such as tetraethylammonium chloride, tetramethylammonium hydroxide and tetramethylphosphonium bromide, and an anti-foaming silicone.
Amount of the slurry in the aqueous polyester solution, that is, the total amount of the hydrophilic polyester and the inorganic particles in the solution is preferably 5 to 50% by weight, more preferably 10 to 40% by weight. A total amount of less than 5% by weight is not preferred because the amount of the slurry added to the thermoplastic resin at the time of production is large inevitably. A total amount of more than 50% by weight makes high the slurry viscosity at the time of converting into the slurry, resulting in reduced workability.
The medium used for preparing a dispersion of the inorganic particles surface-treated with a hydrophilic polyester must be, for example, water and/or an organic compound whose boiling point is lower than the melting point of the thermoplastic resin to which the dispersion is to be added. Water, methanol, ethanol, ethylene glycol, etc. are preferred in view of the economy and handleability. Water is the most preferred medium in view of the safety.
Next, description is made on methods in the present invention for the surface treatment of the inorganic particles with a silicon-containing organic compound. The particles to be treated with a silicon-containing organic compound may be the above-mentioned inorganic particles, but are preferred to be, in particular, silica particles. Therefore, the description on the surface treatment of the inorganic particles with a silicon-containing organic compound is made on a case of the surface treatment of silica particles.
In the surface treatment of silica particles with a silicon-containing organic compound, the number of silanol groups on the surfaces of the silica powder after treatment is preferred to be as small as possible. The number A of silanol groups is preferably 2 xcexcmol/m2 or less, particularly preferably 1.5 xcexcmol/m2 or less. When the number A is more than 2 xcexcmol/m2, the surface treatment of silica particles is insufficient, the silica particles cause agglomeration, and their dispersibility in film is low.
Here, the number A of silanol groups=(silanol group number (xcexcmol/g) on silica particle surface)/(specific area (g/m2) of particle)
The number A of silanol groups on silica particle surface can be determined by titration using trimethylamine. A bulky tertiary amine such as trimethylamine or the like hardly reacts with the silanol groups in the pores of silica particles, owing to the bulkiness, takes part in the interaction between silica particles, and enables measurement of only the silanol groups on the particle surfaces.
The silicon-containing organic compound usable in the treatment of silica particles can be any silicon-containing organic compound which has, at the terminal, functional group capable of bonding with the silanol groups on the silica particle surfaces and further has hydrophobic group. As such a compound, an alkylsilane compound is preferred. As the alkylsilane compound preferably used for the surface treatment of silica particles, there can be mentioned, for example, a halogenosilane, an alkyldisilazane and an alkoxysilane. Specific examples are as follows. The halogenosilane can be exemplified by monomethylchlorosilane, dimethyldichlorosilane and trimethylchlorosilane. The alkyldisilazane can be exemplified by hexamethyldisilazane. The alkoxysilane can be exemplified by trimethylmethoxysilane and dimethyldimethoxysilane. Trimethylmethoxysilane is particularly preferred for the easy handling.
A dispersant can be used for the surface-treated silica particles. The dispersant can be any dispersant as long as it has a polar moiety and a non-polar moiety in the molecule and does not give any adverse effect in the subsequent steps for production of thermoplastic resin composition or in the molded product produced from the composition. The compound having a polar moiety and a non-polar moiety in the molecule can be exemplified by so-called surfactants. There can be used ordinary dispersants and surfactants such as sodium alkylbenzenesulfonate, sodium succinate, sodium alkylphosphate, sodium polycarboxylate, polyoxyethylene alkyl ether and the like. Particularly preferred are sulfonic acid salt compounds and/or carboxylic acid salt compounds such as sodium alkylbenzenesulfonate, sodium succinate and the like.
The amount of the dispersant is preferably 0.01 to 100% by weight, particularly preferably 0.1 to 50% by weight to the silica particles. When the amount of the dispersant is less than 0.01% by weight, it is impossible to disperse the silica particles sufficiently in the polar medium. Meanwhile, an amount exceeding 100% by weight of the dispersant is excessive and is not preferred from an economical standpoint.
The medium used for preparing a dispersion of the surface-treated silica particles is water and/or an inert organic medium whose boiling point is lower than the melting point of the thermoplastic resin to which the dispersion is to be added. Water, methanol, ethanol, ethylene glycol, etc. are preferred in view of the economy and handleability. Water is the most preferred medium for the safety.
Next, description is made on process for producing a thermoplastic resin composition in the present invention. The above-mentioned inorganic particles surface-treated with a hydrophilic polyester or the above-mentioned silica particles surface-treated with a silicon-containing organic compound have very high dispersibility in a thermoplastic resin to which the particles are to be added. Therefore, by using these particles in the form of a dispersion in water and/or an inert organic medium, a thermoplastic resin composition can be obtained using a vented double-screw kneader and extruder.
In the present invention, there is no particular restriction as to the method for feeding an inorganic particles-containing dispersion into a vented double-screw kneader and extruder, as long as the method is efficient, safe and quantitative and does not adversely affect the dispersibility of the inorganic particles. However, in order to remove the water and/or the organic compound whose boiling point is lower than the melting point of the thermoplastic resin, it is necessary that at least one vent hole of the kneader and extruder is kept under reduced pressure. The vacuum of the vent hole is kept preferably at 13,300 Pa or less, more preferably at 6,700 Pa or less, further preferably at 4,000 Pa or less.
In the present invention, regarding the kneading conditions of the vented double-screw kneader and extruder, it is preferred to control the shear stress in a given range. This can be achieved by controlling the melt viscosity of the thermoplastic resin in the shear rate employed during kneading, in a given range. The melt viscosity of the thermoplastic resin is controlled preferably at 10 to 1,000 Pa.S, more preferably at 50 to 500 Pa.S. When the melt viscosity is less than 10 Pa.S, the dispersibility of the inorganic particles added is insufficient. Meanwhile, when the melt viscosity is higher than 1,000 Pa.S, the inorganic particles added are disintegrated and come to have smaller sizes.
According to the process in the present invention, inorganic particles can be contained in a thermoplastic resin uniformly at a high concentration. Therefore, it is possible to produce a thermoplastic resin composition containing inorganic particles in a dispersed state at a high concentration, dilute the composition with a thermoplastic resin containing substantially no particles, and use the diluted composition as a thermoplastic resin composition. In the thermoplastic resin composition obtained by the present process, the inorganic particles cause no agglomeration and are dispersed uniformly. Therefore, when the composition is made into a stretched film, the film has a surface of uniform unevenness free from large projections and is superior in slipperiness and abrasion resistance. The thermoplastic resin composition of the present invention may contain two or more kinds of inorganic particles. The thermoplastic resin composition obtained by the present invention can be made into a single-layered or multi-layered film by a per se known method.
In the present invention, the film produced from the thermoplastic resin composition containing inorganic particles is required to have a friction coefficient of 1.0 or less. When the friction coefficient exceeds 1.0, the film is insufficient in slipperiness when it is wound in a roll form after produced, and the roll has wrinkles, thereby making the winding difficult, with results of reducing productivity significantly and, in an extreme case, losing the commercial value of the film. The film produced from the thermoplastic resin composition is further required to have a film haze satisfying the following formula. When the film haze does not satisfy the following formula, the film is inferior in transparency and is unsuitable for applications such as wrapping and the like.
H less than 0.2T+1.5
wherein H is a film haze (%) and T is a film thickness (xcexc).
This film can be produced by a known method.
For example, a single-layered polyester film can be obtained by subjecting a polyester to melt extrusion form a die, rapidly cooling the extrudate on a cooling drum to obtain an unstretched film, stretching the unstretched film in the longitudinal direction with heating (for example, at a temperature ranging from Tg minus 10xc2x0 C. to Tg plus 70xc2x0 C. (Tg is the glass transition temperature of the polyester)) to obtain a monoaxially stretched film, then stretching the monoaxially stretched film in the transverse direction with heating (for example, at a temperature ranging from Tg to Tg plus 70xc2x0 C.) to obtain a biaxially stretched film, and applying thereto thermal setting and/or thermal relaxation. The resulting biaxially oriented film preferably has a thickness of 0.5 to 150 xcexcm, particularly preferably 1 to 100 xcexcm. The draw ratio of the film differs depending upon the application, but both the longitudinally stretching ratio and the transversely stretching ratio are preferred to be 2 to 6. The thermal setting and/or the thermal relaxation can be conducted by a known means under known conditions, depending upon the application of the film.
A double-layered polyester film can be produced in the same manner as above mentioned method and conditions employed for the single-layered polyester film except that two kinds of polyesters are subjected to co-extrusion to obtain an unstretched double-layered film.
According to the present invention, inorganic particles can be added to a thermoplastic resin easily; therefore, there can be provided a thermoplastic resin composition wherein inorganic particles are dispersed in a thermoplastic resin at a high dispersibility, a process for production thereof, and a biaxially oriented film produced from the composition.